Where's the shoulder in the film data sheets?

Discussion in 'B&W: Film, Paper, Chemistry' started by Rudeofus, Sep 15, 2011.

  1. Rudeofus

    Rudeofus Subscriber

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    If I look at the data sheets of current b&w film stock as published by Kodak, Fuji and Ilford, they all contain characteristic curves which show the whole toe but never the shoulder. For some reason all these published characteristic curves stop somewhere in the straight section.

    Given how much fuzz most reputable b&w photography books make about the shoulder of film, is there a special reason the shoulder is not shown in data sheets?
     
  2. David Lyga

    David Lyga Subscriber

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    That is a good question and maybe both of us are wholly naive. But...perhaps there is far more importance in establishing the threshold of exposure (toe) and that the 'flattening out' with excess exposure comes about ONLY with too much exposure. With films like microfilm (ie, Kodak's ImageLink) there is not enough latitude for both shadow detail and highlight detail. You must choose one or the other. But with films like Tri-X, HP-5+, etc, there can be an abundance of overexposure before the shoulder flattening becomes too apparent.

    If I make no sense perhaps someone will come to our collective rescue. - David Lyga

    MODERATOR: I cannot remove the double 'there' in my second sentence. In the 'edit' mode only one appears and if I remove that one, none remains. - David Lyga
     
  3. Monito

    Monito Member

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    Refresh your page. (IAmNotAMod)
     
  4. David Lyga

    David Lyga Subscriber

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    Sorry, I am too stupid and don't know how! - David Lyga
     
  5. Monito

    Monito Member

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    Usually it is Shift F5. But in any case, explore the menus of your browser, something you should have done a while ago. Look for "Refresh" or "Reload". Do it when you have this page open (not editing).

    In the recent FireFoxes, it is not in the menu, but Shift F5 works. In any case it is in the toolbar as a circular arrow.
     
  6. ic-racer

    ic-racer Member

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    The usual 21 step wedge does not give enough datapoints to show both the toe and shoulder on modern films. I have used a wide 21 step wedge that was half-sandwiched with a strong ND filter to try and make "complete" curves.

    Sure, people post about "The Shoulder" but sometimes it is crazyass stuff. For example the guy exposing T-max 400 at ISO 3200 shooting with a hazy f1.2 lens from e-bay wide open with a dirty "Skylight filter" (maximum flare condition & severe underexposure) and worrying about his highlights on the shoulder. Under those conditions the highlights are likely to fall TEN or more stops from the shoulder.
     
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  7. Rudeofus

    Rudeofus Subscriber

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    And I'm quite sure that Kodak, Fuji and Ilford have better tools available than limited range step wedges and ND filters. And even in the absence of such tools you can create the full curve with two or three separate measurements. It may be less neat that way but it's just for a data sheet after all. The curves in the data sheets end at densities below 3, even a 200€ flat bed scanner could measure this.
    Even Ralph Lambrecht and Ctein write about the shoulder and the importance of its shape, so this topic is not exactly reserved for a bunch of clueless freaks ...

    There are some situations where I would really like to know in advance how certain films are going to respond to severe local overexposure, e.g. any scene including the sun during broad daylight or any scene including the moon at night.
     
  8. Photo Engineer

    Photo Engineer Subscriber

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    If you look at a standard H&D curve, for negative films the shoulder is on the right where the straight line ends and density levels off. On reversal films, the shoulder is on the left where density levels off. Usually, this is about D=3.0 but in negative films and MP print films it can be higher or it may not even be present due to extreme latitude.

    PE
     
  9. michael_r

    michael_r Subscriber

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    I prefer to do my own tests and do them in-camera with a white/grey card. I plot from threshold up to 10 stops above metered (once I've determined my exposure index). It gives me a full scale curve. Personally I've never found the H&D curves in Kodak, Ilford, or Fuji datasheets to be of much use.
     
  10. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    It sort of depends on the film and on the way the manufacturer plots their graphs.

    If you look at the curves in attachment here, Plus-X has a clear shoulder, followed by Tri-X. Then PanF+ has a very gentle shoulder (use a straight line to compare) and HP5+ has almost no visible shoulder.
     

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  11. ic-racer

    ic-racer Member

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    The shape of the shoulder is of no importance if there is no image forming data there. What are you taking pictures of that places density way out there? Light sources?
     
  12. Rudeofus

    Rudeofus Subscriber

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    Here:

     
  13. Rudeofus

    Rudeofus Subscriber

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    Yes, and unfortunately only very few characteristic curves posted in data sheets show that shoulder. If you look at the curves Michael posted (and the like of which can be found in most data sheets), the curves suddenly end in the straight section with no shoulder in sight.

    You mean the film goes up in flames if you expose it more? At some point all the silver must be activated and reduced by the developer, so there must be some form of well defined shoulder in every negative film.
     
  14. Photo Engineer

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    This is not actually correct. Films can be designed to have a straight line up to densities of 6.0 or greater, but they are never needed in practice. A density of 3.0 - 4.0 is generally enough and the curves posted generally encompass enough latitude for overexposure by as much as 2 stops. As you push into the shoulder, you lose detail, of course. The same is true of the toe. Neither can be totally eliminated.

    Sometimes more detail is lost by the printing process than by overexposure of the negative, and this can only be corrected by creative printing (split grade printing and / or dodging and burning)

    PE
     
  15. ic-racer

    ic-racer Member

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    I'll explain what I have done in more detail. I have a 21 step wedge that is over twice as wide as my densitometer aperture. I cover 1/2 of the step wedge with a strong ND filter so that I am left with 42 boxes, each slightly larger than my densitometer aperture. I use that to make the exposure.

    However, there are technical hurdles. For example you need very tight contact or else it bleeds too much from the strong light needed to make the exposure. The soft foam of an EG&G is not enough pressure.

    Also, the exposure duration needs to be much longer than one would use for a H&D curve made with a 21 step wedge, so you may need multiple pops of the sensitometer flash, thus straying from the realm of any presumed ISO testing condition.

    Another way to put it is that with a sensitometer calibrated for ISO testing, the light may not be strong enough to get the film to the shoulder even without any added density. You understand that the last step of the wedge is clear, so you can't just make it "more clear" if you know what I mean.
     
  16. Rudeofus

    Rudeofus Subscriber

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    So what you say is the characteristic curve published in the data sheet is meant for the zone system disciples who need 10 stops and no more, so the curves show a little more than that to cover exposure errors. It also appears that film goes way beyond the density range shown in these curves but much higher densities would require multi mega watt enlarger lamps (log10 is one flat curve).

    Thanks all for the clarification!
     
  17. Photo Engineer

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    No, I did not say that! I did not mention the zone system and we never used it at EK AFAIK.

    The curve as you see it is normally truncated at about D= 3.0 because that is what is normally used. Also, it might be that the normal curve that goes higher than that is larger than a sheet of 8.5 x 11" paper that we use for plotting. In fact, I have drawn larger curves horizontally by taping 2 sheets together.

    But, what is on the shoulder does not matter as D=3.0 for example and is unchanged. On the shoulder itself, you can modify it during printing as I noted above.

    But, as you say, it is mainly due to the fact that at extremely high densities you have, as you say, long printing times or bright bulbs!

    Again, the zone system is not really involved here.

    PE